Method and apparatus for straightening sheet materials



Oct. 27, 1970 1-. SEVENICH EI'AL 3,535,902

METHOD AND APPARATUS FOR STRAIGHTENING SHEET MATERIALS Filed Feb. 29,1968 T E QOK SEVtE V IQH PE'FER ZEN-5 United States Patent Ofice3,535,902 METHOD AND APPARATUS FOR STRAIGHTEN- ING SHEET MATERIALSTheodor Sevenich, Dortmund, and Peter Zens, Dortmund-Kirchderne,Germany, assignors to Hoesch Aktiengesellschaft, Dortmund, Germany FiledFeb. 29, 1968, Ser. No. 709,351 Claims priority, application Germany,Mar. 6, 1967,

1,602,461; Sept. 21, 1967, 1,602,468

Int. Cl. B21d 1/02 US. Cl. 72-160 8 Claims ABSTRACT OF THE DISCLOSUREStraightening sheet materials, especially sheet metal having at least acurvature in the transverse direction, by passing the sheet in acontinuous movement in its longitudinal direction between two sets ofstraightening rollers having concave and convex outer surfaces,respectively, which act under pressure upon the convex and concave sidesof the sheet, respectively, so as to eliminate said curvature.

The present invention relates to a method and an apparatus forstraightening sheet materials and especially sheet metal which has acurvature extending transverse to the direction in which the materialhas been rolled in a hot-rolling mill.

In the production of sheet metal of any width it is the conventionalprocedure to wind the rolled sheet coming from the rolling train andwhile still in a hot condition into a coil and then, after it hascooled, to unwind it from the coil in a cutting apparatus in which it iscut transversely and/or longitudinally to the rolling direction to thedesired dimensions. While being unwound from the coil, the sheetmaterial is straightened and thereby plastically deformed in thelongitudinal direction. This straightening operation, however, cannotprevent that residual stresses remain in the longitudinal direction ofthe sheet material and that the transverse components of theselongitudinal stresses will cause the material to curve in the transversedirection. These transverse curvatures must be thereafter eliminated ina separate straightening operation outside of the cutting apparatus.

For straightening uneven parts of metal sheets, these sheets aregenerally passed through straightening machines which may be ofdifferent types. In one type of these machines the sheet material ispassed between two superimposed rows of cylindrical straighteningrollers which are rotatable in opposite directions and apply a pressureupon the opposite sides of the sheet. Another known type of thesestraightening machines comprises cylindrical straightening rollers whichare bent by means of bracing rollers so that the sheet material runningtherethrough will be stretched longitudinally at certain areas wherebythe waviness of adjacent areas of the sheet will be eliminated. Stillanother known type of straightening machines comprises short camberedstraightening rollers which may be shifted axially on their shafts andact upon the particular areas of the sheet which are to be straightened.There is also a straightening method known in which two different typesof these machines are combined so that the sheet metal is at firststraightened in its longitudinal direction and thereafter in a separateoperation in the transverse direction by means of a flexiblestraightening roller or a short straightening roller.

In all of these known methods the sheets to be straightened will bedeformed in their direction of travel while the deformation which isattainable in the transverse direction is very small as compared withthe longitudinal deformation. If it is necessary to eliminate transversePatented Oct. 27, 1970 curvatures in the sheets, the latter must bepassed several times through the straightening machine. Since repeatedstraightening operations cannot be carried out at all or only with greatdifiiculty in a cutting apparatus, the known straightening methods andthe machines for carrying out these methods are unsuitable forcontinuously eliminating the transverse curvatures of metal sheets.

It is an object of the present invention to overcome the above-mentioneddisadvantages of the known straightening methods and apparatus and toprovide a new straightening method in which sheets or strips of metal orother materials will be completely straightened in the longitudinal andtransverse directions by being passed only once through a new type andarrangement of straightening rollers.

For attaining this object, the invention provides that the sheets orstrips to be straightened are given an initial stress contrary to thetransverse curvature and are deformed beyond the elastic limit of thesheet material by a rolling operation in the longitudinal direction inwhich they are produced by the rolling train of the mill. The extent towhich the elastic limit of the material is to be exceeded in thetransverse direction of the sheet is preferably determined by the sum ofthe transverse components of the longitudinal stresses and of theinitial stress itself which the sheet has in its transverse direction.

The stresses which according to the invention are produced in thetransverse direction of the sheet should, however, preferably be keptfar :below the elastic limit of the material since they are not neededto effect a plastic deformation of the material in the transversedirection. The transverse curvature of the sheets is thereforeeliminated merely by plastically deforming the material in thelongitudinal direction to such an extent that the transverse componentsof the stresses which are produced by this longitudinal plasticdeformation will be sufficiently increased by the transverse stressesthemselves.

For straightening sheets or strips especially of metal by a singlecontinuous operation, the invention provides an apparatus whichcomprises two rows of associated straightening rollers which aredisposed within two different levels and are provided with concave orconvex outer surfaces, respectively. The straightening rollers withconvex surfaces are preferably provided in the upper row and thestraightening rollers with concave surfaces in the lower row since thesheets are preferably passed through these rollers with their transversecurvature extending in the upward direction. Since according to the newmethod only a small stress is to be produced in the transverse directionof the sheet or strip material, the degree of curvature in the axialdirection of the straightening rollers is prefera bly made very large.The diameter of these straightening rollers and their distances fromeach other therefore have to be only slightly larger than those of theconventional cylindrical straightening rollers in order to attain therequired permanent plastic deformation of the sheets in theirlongitudinal rolling direction for completely straightening the sheetsin all directions.

The features and advantages of the present invention will become moreclearly apparent from the following detailed description thereof whichis to be read with reference to the accompanying diagrammatic drawings,in which FIG. 1 shows a perspective view of a complete set ofstraightening rollers according to the invention;

FIG. 2 shows a perspective view of a plate, for example, of sheet metalwhich has been wound from a coil and cut off transversely;

FIG. 3 shows a perspective view of a set of straightening rollersconsisting of two upper convex rollers and one lower concave roller forcarrying out the first stage of the straightening operation;

FIG. 4 shows the lines of force in a sheet while the sheet is being bentabout the lower concave straightening roller according to FIG. 3;

FIG, shows a perspective view of a set of straightening rollersconsisting of one upper convex and two lower concave rollers forcarrying out the second stage of the straightening operation; while FIG.6 shows the lines of force in a sheet, for example, of metal, while thesheet is being bent about the upper convex straightening rolleraccording to FIG. 5.

For carrying out the new method of straightening sheets or strips, forexample, of metal, the invention provides a set of straighteningrollers, as diagrammatically illustrated in FIG. 1, which comprises arow of lower rollers 1 with concave outer surfaces and a row of upperrollers 2 with convex outer surfaces. All of these straightening rollersl and 2 are ground so as to have substantially equal concave or convexcurvatures 0, respectively, as indicated in FIG. 3.

FIG. 2 illustrates a sheet, for example, of metal 3 which has beenunwound from a coil and has then been cut transversely to the desiredlength. This sheet has a curvature a in its longitudinal direction and acurvature b in the transverse direction. Both these curvatures a and bare to be straightened so that the sheet will be completely plane. Forthis purpose, the invention provides that in a first working stage thesheet is passed through the set of straightening rollers as shown inFIG. 3. This first part of the straightening operation gives the sheetan initial tension in the direction opposite to the original transversecurvature b by bending it for the distance b+c. This results in acompressive stress A on the upper side of sheet 3 and in a tensilestress A on its lower side, as indicated by the solid arrow heads inFIG. 4. These stresses A and A by themselves do not exceed the elasticlimit of the material. In the longitudinal direction of sheet 3, thestresses A and A produce the stress components B and B as indicated inFIG. 4 by ordinary open arrow heads. The stress component B on the upperside of the sheet forms a tensile stress and the stress component B onthe lower side of the sheet a compressive stress. The stress componentsB and B by themselves likewise do not reach the elastic limit of thematerial.

When the sheet 3 runs through the system of straightening rollersaccording to FIG. 3, it will be plastically deformed in the longitudinaldirection about the lower concave straightening roller. This results ina tensile stress C on the upper side of the sheet and a compressivestress C on its lower side, as indicated by the double open arrow headsin FIG. 4. In the transverse direction of the sheet, the stresses C andC produce the stress components D and D as indicated by triple openarrow heads in FIG. 4. Since the stress component D on the upper side ofthe sheet is a compressive stress, it is added to the initial stress Awhile the stress component D is a tensile stress and therefore likewiseadded to the initial stress A If the sheet is plastically deformed to asufficient extent in the longitudinal direction of the stresses C and Cthe sums of the stresses of the components A and D and of the componentsA and D will also exceed the elastic limit of the material in thetransverse direction and a plastic deformation of the sheet will takeplace in the transverse direction which eliminates the originalcurvature b of the sheet. The curvature a in the longitudinal directionof the sheet will, however, at first be increased by the straighteningoperation by means of the straightening rollers according to FIG. 3.

Since the entire roller arrangement as illustrated in FIG. 1 consists ofseveral convex straightening rollers in the upper row and severalconcave straightening rollers in the lower row, the first stage of thestraightening operation as above described will be followed immediatelyby the second stage by means of the roller arrangement according to FIG.5. In this second straightening stage, the sheet will be stressed in thetransverse direction in the same manner as in the first straighteningstage according to FIG. 3. By bending the sheet in the transversedirection, the compressive stress E will be produced on the upper sideof the sheet and the tensile stress E on its lower side. These stressesare indicated in FIG. 6 by single open arrow heads. When runing throughthe roller arrangement according to FIG. 5, sheet 3 will be bent in thelongitudinal direction about an upper convex roller 2. The stresses Gand G which are then produced are indicated in FIG. 6 by double openarrow heads. These longitudinal stresses G and G produce the transversecomponents H and H in the transverse direction, as indicated in FIG. 6by triple open arrow heads. As may also be seen in FIG. 6, the stressesE and E extend in the opposite direction to the transverse components Hand H Therefore the transverse components H and H will reach the elasticlimit of the material only after the latter has been plasticallydeformed in the direction of the longitudinal stresses G and G to agreater extent than that which occurs during the passage of the sheetthrough the roller arrangement according to FIG. 3 in which thetransverse components D and D are formed which are produced by thelongitudinal stresses B and B as indicated in FIG. 4. The rollerarrangement according to FIG. 5 thus not only bends back the sheet so asto eliminate its deformation in the longitudinal direction which wasproduced by the preceding straightening stage by means of the rollerarrangement according to FIG. 3, but it also eliminates the curvature awhich originally existed in the longitudinal direction. The order ofsuccession in which the individual straightening stages may be carriedout may also be reversed and, if necessary or desirable, they may berepeated several times.

The considerable advantage of the straightening method according to thepresent invention over the straightening methods as heretofore known isparticularly the fact that the transverse curvature of a sheet or stripof metal of other material may be completely eliminated by passing itonly once through the set of straightening rollers according to FIG. 1.It is another advantage of the new method that it also permits thedifferent transverse curvatures of sheets and strips of differentthicknesses to be completely eliminated by means of the same uniformlyground straightening rollers and by merely adjusting the upper and lowerstraightening rollers relative to each other so as to exert the requiredpressures upon the sheets or strips in accordance with their differentthicknesses. If the method according to the invention is applied, it istherefore no longer necessary to carry out any additional expensivestraightening operations outside of the cutting apparatus.

Although our invention has been illustrated and described with referenceto the preferred embodiment thereof, we wish to have it understood thatit is in no way limited to the details of such embodiment but is capableof numerous modifications within the scope of the appended claims.

Having thus fully disclosed our invention, what we claim is:

1. A method of straightening sheets or strips of metal or othermaterials having at least a curvature transverse to their longitudinaldirection of travel through a rolling train or other apparatus in whichthey have been produced, wherein a pressure is exerted upon said sheetsin the direction opposite to said transverse curvature and said sheetsare deformed in said longitudinal direction beyond the elastic limit oftheir material, whereby said sheets are bent so as permanently toeliminate said transverse curvature.

2. A method as defined in claim 1, wherein said pressure is exerted uponsaid sheets and said sheets are deformed by passing said sheets in onecontinuous movement in said longitudinal direction between two sets ofrotating straightening rollers having concave and convex outer surfaces,respectively, and pressing said convex rollers upon the concave side ofsaid sheets and said concave rollers upon the convex side of saidsheets.

3. A method as defined in claim 1, wherein said elas tic limit isexceeded to an extent determined by the sum of the transverse componentsof the longitudinal stresses and the transverse stresses of said sheets.

4. An apparatus for straightening sheets or strips of metal or othermaterials having at least a curvature transverse to their longitudinaldirection comprising a set of at least two upper straightening rollersand a set of at least two lower straightening rollers rotatable aboutsubstantially parallel axes, each roller of one set being positionedclosely adjacent a roller of the other set, each roller of one of saidsets having a concave outer surface and each roller of the other sethaving a convex outer surface, whereby when said sheets or strips arepassed in a continuous movement between said two sets of rollers in saidlongitudinal direction and substantially transverse to the axes of saidrollers, they are straightened in the longitudinal and transversedirections thereof.

5. An apparatus as defined in claim 4, wherein said concave and convexrollers have substantially the same degree of curvature.

6. An apparatus as defined in claim 4, wherein said rollers of saidupper row have a convex outer surface and said rollers of said lower rowhave a concave outer surface.

7. An apparatus as defined in claim 4, wherein one of said sets has atleast three rollers, two of said three rollers cooperating with each ofthe rollers of the other set.

8. An apparatus as defined in claim 4, wherein each roll of one set hastwo rolls of another set cooperating therewith and the axes of the rollsof each set are located substantially in a single plane, the planesbeing parallel.

References Cited UNITED STATES PATENTS 1,584,499 5/1926 Zachhuber 72-176X 1,854,021 4/1932 Derby 72-176 X 2,240,548 5/1941 Cairns 72179 X2,337,047 12/1943 Hunter 72-179 2,348,539 5/1944 Harper 72176 2,470,2355/ 1949 Burrell 72-179 X 2,692,003 10/1954 Nieman et a1. 72-1792,854,056 9/1958 Stanius 72-176 X MILTON S. MEHR, Primary Examiner US.Cl. X.R.

